In a sense, we shouldn’t be surprised: he is by some distance (as I noted in June) the most articulate and sure-footed of the four candidates, and offers an infectious hope and ambition.

But the hysteria will subside and Labour will return to its senses. I have no special insight into this contest, beyond my conviction that realism will wrest back control of the party from the hyper-ideologues fuelling Corbynmania.

Fantastical political upheaval is a rare occurrence, and I think its finite supplies were probably exhausted by the 7 May general election result.

True, there are polls showing Corbyn in the lead on first preferences. None, not even the slightly dodgy leaked private polls, has yet shown him in a convincing lead after second and third preferences are accounted for. And it seems plausible that such polls will end up over-stating the likelihood of younger eligible Labour voters — the core Corbynites — actually to cast their ballot: ‘lazy Labour’ inflated the party’s support in the national polls, and are probably flattering Corbyn’s internal numbers now.

(Of course, there is a difference between the electorate of the general public and the selectorate of signed-up Labour members, registered supporters and trades union affiliates. You would expect the latter to be more politically engaged. That’s the hypothesis sustaining Corbyn’s status as favourite. I’m dubious. But I may very well be wrong.)

The battle for second place — between Andy Burnham and Yvette Cooper — is, I reckon, the battle to top the poll. The numbers surely favour Cooper. She is more or less tied with Burnham in nominations from constituency Labour parties (CLPs). With Liz Kendall destined to trail in fourth, most of her votes will transfer to Yvette, the next-most moderate (and the other female) candidate.

My assumption would be there will be a straight run-off between Corbyn and Cooper. My expectation is that Cooper will carry that, comfortably. (I don’t entirely rule out the run-off being between Burnham and Cooper, by the way.)

If that happens, the Westminster commentariat will exhale a disappointedly muted sigh. She’ll be no fun. Yvette Cooper is remorselessly middle-of-the-road, more or less competent, too indecisive to sound extremist, unmemorably articulate. Labour will tread water quite efficiently with her as leader. If the Tories screw up, her ‘one more heave’ approach might even enjoy the last laugh.

Political parties, at least ones which aspire to exercise power, should choose the leader their opponents most fear. I’m not sure the Tories are exactly frightened by the spectre of Yvette Cooper. But they would regret the extinguishing of Labour’s current death-wish to write off 2020 as unwinnable by electing the unelectable (to be clear: either Corbyn or Burnham are squarely in that category), thus making 2025 unwinnable, too.

I recently asked the non-Labourites on my Twitter timeline — see my Storify below — who they thought would be the best (or least worst) leader for Labour.

Overwhelmingly the answer was Cooper. She won’t set the world alight, but she won’t split the party either, was the gist. Labour will survive intact until a new, more inspiring candidate emerges. That seems the best they can hope for right now.

And while the Labour leader race is the one dominating the headlines, it is the deputy leadership which may prove at least as significant to Labour’s long-term future.

Tom Watson looks certain to win. There is a Good Tom: the fearless backbencher willing to champion the underdog (phone-hacking/child abuse victims) against the powerful (tabloids/the ‘Establishment’). And there is a Bad Tom: the Unite-backed fixer wanting to exert real grip on his party’s candidate selection. I admire the former, but it looks like the latter is in the ascendant.